The present invention relates to a thermal development image forming apparatus having a sheet correcting unit for correcting positions or directions of overlapped thermal development/transfer sheets.
A method of obtaining a color image by releasing a diffusion pigment by thermal development, and separating a silver image from the pigment by transferring the pigment onto an image-receiving element has already been proposed. In addition, a variety of techniques associated with photosensitive elements, image-receiving elements, a thermal development method, and apparatuses therefor have been disclosed.
As an apparatus using such a development method, a dry color hard copying machine disclosed in, e.g., Japanese Patent Laid-Open (Kokai) No. 62-201433 or the like is proposed. According to this apparatus, a color image is formed on an image receiving sheet in the following manner. A latent image is formed first by exposing a photosensitive element coated on a photosensitive sheet. The photosensitive sheet is overlapped on the image-receiving sheet, and the sheets are clamped between a rotary drum and an endless belt which is urged against the drum. A diffusion pigment of an image portion is then released from the photosensitive sheet by heating and pressing the sheets, and the sheets are separated upon transfer of an image onto the image-receiving sheet.
As described above, in the final process, both the sheets are separated. Various separation schemes are employed. For example, Japanese Patent Laid-Open (Kokai) No. 61-18951 discloses an automatic separating unit, as shown in FIG. 5.
In this apparatus, the width of an image-receiving sheet P1 is set to be greater than that of a photosensitive sheet N1. In addition, the sheets N1 and P1 are overlapped while the leading end of the sheet N1 is caused to protrude from that of the sheet P1. When the leading end of the sheet N1 reaches a position above a separating roller 1, the roller 1 is quickly moved upward, thus separating the sheet N1 from the sheet P1. In this case, both the sides of the sheet P1 are clamped/supported by two pairs of clamping rollers 2 and 2' so as to allow the sheet P1 to resist a separating force acting on the sheet N1.
According to a separating unit proposed in Japanese Patent Laid-Open (Kokai) NO. 63-159850 by the present inventor, as shown in FIG. 6, a protrusion 3 is formed at a central leading portion of a photosensitive sheet N2 in advance, and the protrusion 3 is caused to protrude from a leading end 4 of an image-receiving sheet P2 and the leading end 4 is caused to protrude from leading portions 3a on both the sides of the protrusion 3 when the sheets N2 and P2 are overlapped. Separation of the sheets N2 and P2 upon completion of thermal development/transfer is performed as follows. The central leading portion (protrusion) 3 of the sheet N2 is clamped by a feed roller pair (not shown) after the sheets N2 and P2 pass through pressing rollers 5 and 6. At the same time, both side leading portions 4a of the sheet P2 are positioned under wedge-like separators 7 and 7'. The feed roller pair clamping the central leading portion 3 is moved upward, and the separators 7 and 7' are moved downward. That is, separation of the sheets N2 and P2 is performed from their leading portions by using the pressing rollers as pressing members for resisting a separating force. The separation of the sheets N2 and P2 is continued afterwards while a feed speed is increased.
In each separation scheme, in order to properly perform separation, overlapped sheets must be sent in a separating unit in a proper direction. If the sheets are not properly positioned, troubles, such as a jam and incomplete separation of the overlapped sheets, may be caused.
In addition, in the conventional apparatuses, a sheet fed in a thermal developing section tends to be incorrectly positioned, and hence is skewed from a feed direction by, e.g., 2 mm. Development and transfer are often performed in such a state. As a result, degradation in appearance due to misregistration of an image transferred onto an image-receiving sheet or degradation in sheet separation precision upon transfer frequently occurs as well as other troubles.